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"Describe one method by which the distance to stars from Earth is measured, and one modern improvement to this method which increases its accuracy."

A: One common method used to measure the distance of stars from the Earth is Stellar Parallax. Here, we measure our chosen star’s apparent movement relative to another background star. We say “apparent”, because it’s not really the star moving - it’s us on Earth rotating along with the planet!

And this is precisely what we use to our advantage: after a half-orbit around the sun - registered as 6 months for us - we will note that our star will have “moved” relative to the background stars (keep in mind that these background stars are far enough to assume negligible relative motion for them). We will measure the angle subtended during this motion, with the units of arc seconds. Then, it is simply a matter of inserting this parallax angle p in the following equation:
d = 1/p
Where d = distance between star and Earth, in parasecs
P = parallax angle, in arc seconds

An improvement to this technique has been introduced by using telescopes that are situated in Earth’s orbit, rather than on its surface. That way, any possible interference with the atmospheric layers can be avoided.

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